JPH01225091A - High-frequency heating device - Google Patents

Abstract

PURPOSE:To extend the life of a magnetron by reducing the input power when the temperature of the magnetron rises and the operating voltage is reduced due to the temperature rise of the device or the like. CONSTITUTION:An inverter circuit 7 converting a DC power source into the high-frequency power by high-frequency switching, a high-frequency oscillator applied with the high-voltage power to oscillate high frequencies, a rectifying circuit rectifying the secondary winding output of a current detecting transformer 11 connected to the commercial power line via the primary winding, and a low-pass filter 14 cutting off the high-frequency component of the output of a terminating circuit 13 terminating the output of this rectifying circuit are provided, the switching operation of a switching element 5 is controlled so that the maximum value of the ripple output voltage of the low-pass filter 14 becomes the preset value. When the temperature of a magnetron 10 rises and the operating voltage is reduced, the input power is reduced, thereby the life of the magnetron is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the improvement of high-frequency heating devices such as microwave ovens that heat foods and liquids by so-called dielectric heating. The present invention relates to a high-frequency heating device configured to supply high-voltage power applied to a device (described below) using high-voltage power obtained from an inverter circuit using switching elements such as transistors, a high-voltage transformer, etc.

In a conventional magnetron, its operating voltage (anode-dorak voltage): VAK is determined by the magnetic flux of a pair of magnets, so when the temperature of the magnet increases, the magnetic flux from the magnet decreases, and AAK decreases.

In addition, the input power of a magnetron is expressed as the product of AAK and IAK (anode current), so if the input power is controlled to be constant using inverter circuit technology, VAK will decrease as the magnetron temperature rises. , IAI
rises.

Since most of the heat generated by the magnetron is determined by the value of IAK, an increase in IAK further accelerates the temperature rise of the magnetron, resulting in a reduction in its life.

Problems to be Solved by the Invention Therefore, when controlling the input power to the magnetron at a constant level, the problem arises that when the temperature of the magnetron increases, the IAI increases and its lifespan decreases, and some countermeasure is required. be.

Means for Solving the Problems Accordingly, the present invention includes a power supply unit that rectifies a commercial power source and converts it into a DC power source, an inverter circuit that converts the DC power source into high frequency power by high frequency switching using a switching element, and a power supply unit that converts the high frequency power into a high frequency power source. A high-voltage transformer that boosts the voltage and converts it into high-voltage power, a high-frequency oscillator that applies the high-voltage power and oscillates a high frequency, a current detection transformer that has a primary winding connected to the commercial power line, and a secondary winding of the current transformer. a rectifier circuit that rectifies the line output, a termination circuit that terminates the output of the rectifier circuit with a resistor, a low-pass filter that blocks high frequency components of the output of the termination circuit, and a maximum value of the ripple output voltage of the low-pass filter is predetermined. The above-mentioned problem is solved by comprising a power control circuit that controls the switching operation of the switching element so that the value of .

Function: With this configuration, when the temperature of the magnetron increases and YAK decreases, the input current from the commercial power supply is reduced and the input power is lowered. has a longer lifespan.

Embodiment FIG. 1 shows a circuit configuration of a high-voltage power generation section of a high-frequency heating apparatus according to a first embodiment of the present invention.

A power supply unit 4 that rectifies a commercial power supply 1 with a first rectifier circuit 2 and converts it into a DC power supply 3; an inverter circuit 7 that performs high frequency switching of this DC power supply 3 with a switching element 5 and converts it into a high frequency mino J6; A high-voltage transformer 9 that boosts the high-frequency power 6 and converts it into high-voltage power 8, a magnetron 10 that applies this high-voltage gravity 8 and oscillates high-frequency waves, and a current detection transformer that has a primary winding 118L connected to one commercial power supply line. 11, a second rectifier circuit 12 that rectifies the output of this secondary winding 11b, and a termination circuit 13 that terminates the output.
, a low-pass filter 14 that blocks high-frequency components of its output, a first comparison circuit 16 that compares its output with a reference signal 15 , and a charging/discharging circuit that charges and discharges a capacitor 18 using its output and a low-voltage power supply 17 . 19, the voltage of the capacitor 18, and the output of the saw wave generation circuit 20 are compared to create a drive pulse 21 for the switching element 5.
It is composed of a comparison circuit 22.

With this configuration, when the temperature of the magnetron is constant, the output of the low-pass filter 14 increases, that is, when the input current from the commercial power supply 1: Iin increases, the ON time of the switching element is decreased, and Iin is lowered. Conversely, when Iin decreases, the ON time is increased to increase Iin, thereby controlling the input power to be constant.

Conventionally, when the temperature of the magui and tron 10 increases due to an increase in the temperature of the controlled frequency wave heating device (VAK increases by 1 degree), the power in is constant, but in the present invention, the As shown in the temperature characteristic diagram, Iin decreases. That is, the temperature of the magnetron is controlled to be lowered by suppressing an increase in IAP.

This seems to be because, as shown in FIG. 3, the period during which Iin flows during a half cycle of the commercial power supply 1 expands as the temperature increases, and this expanded component is also taken into account in the output of the low-pass filter 14.

Similarly, as shown in the AEN waveform diagram in Figure 3, when the commercial power supply voltage 1 voltage: Vin changes, when Win increases, I
The period in which in flows is expanded, but in this case as well, conventionally Ii
Although it is rare for n to be constant, in the present invention, as shown in the voltage fluctuation characteristic diagram in FIG.
Control is performed to lower the temperature of the magnet (magnet) and at the same time to reduce changes in input power.

FIG. 5 is a partial operational waveform diagram. Iin flows in synchronization with each half cycle of Vin, and the ripple component included in the output of the low-pass filter 14 also synchronizes with this synchronization. The peak value of the output of the low-pass filter 14 substantially coincides with the reference signal 15 due to the principle of circuit operation.

Figure 6 shows a high voltage capacitor 23 on the secondary side of the high voltage transformer 9.
This is a partial circuit configuration diagram of a second embodiment in which a high-voltage rectifier circuit 25 consisting of a high-voltage diode 24 and a high-voltage rectifier circuit 25 are inserted. The circuit operates in the direction of reducing Iin even when vin increases.

In addition, in FIG. 1, the number of elements of the second rectifier circuit 12,
It goes without saying that the same operation can be expected even if the number of stages of the low-pass filter 140, the configuration, and other circuit configurations are different from those shown.

Effects of the Invention As described above, in the high frequency heating device according to the present invention, when the temperature of the magnetron increases due to an increase in the temperature of the device, Ii
Since input power is lowered by narrowing down n, the life of the magnetron is extended.

Additionally, even when Vin increases, Iin is similarly reduced to lower the input power, thereby extending the life of the magnetron and at the same time reducing fluctuations in human power.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the pressure power generation section of the high-frequency heating device according to the first embodiment of the present invention, Fig. 2 is a temperature fluctuation characteristic diagram, Fig. 3 is a 1 inch waveform diagram, and Fig. 4 is the same voltage. A fluctuation characteristic diagram, FIG. 5 is a Vin+Iin waveform diagram, and FIG. 6 is a partial circuit diagram according to the second embodiment. 1...Commercial power supply, 3...DC power supply, 4.
...Power supply section, 5...Switching element, 6
...High frequency power, 7...Inverter circuit, 8
...High voltage power, 9...High voltage transformer,
10... Magne 1-ron, 11... Current detection transformer, 12... Second rectifier circuit, 13
... Termination circuit, 14 ... Low pass filter, 15 ... Reference signal. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 4
Figure 0-7ri°Netron

Claims (1)

[Claims] A power supply unit that rectifies commercial power and converts it into DC power; an inverter circuit that converts the DC power into high-frequency power by high-frequency switching using a switching element; and a high-voltage transformer that boosts the high-frequency power and converts it into high-voltage power. , a high frequency oscillator that oscillates high frequency waves by applying the high voltage power;
a current detection transformer having a primary winding connected to the commercial power supply line; a rectifier circuit that rectifies the secondary winding output of the current transformer; a termination circuit that terminates the output of the rectifier circuit with a resistor; A high-frequency heating device comprising: a low-pass filter that blocks high-frequency components of the output; and a power control circuit that controls the switching operation of the switching element so that the maximum value of the ripple output voltage of the low-pass filter becomes a predetermined value.